Accumulated Other Comprehensive Income (Changes in AOCI by Component) (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2020		Mar. 31, 2019
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance		$ 40,367		$ (35,305)
Other comprehensive income before reclassifications	[1]	97,673		36,873
Amounts reclassified from accumulated other comprehensive income (2)	[1]	(833)		1,478
Net current-period other comprehensive income	[1]	96,840		38,351
Ending balance		137,207		3,046
Unrealized Gains and Losses on Available-for-Sale Debt Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance		33,038		(33,128)
Other comprehensive income before reclassifications	[1]	79,696		32,063
Amounts reclassified from accumulated other comprehensive income (2)		(191)	[2]	1,417	[1]
Net current-period other comprehensive income	[1]	79,505		33,480
Ending balance		112,543		352
Unrealized Gains and Losses on Pension Plan Liability [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance		(3,974)		(2,177)
Other comprehensive income before reclassifications	[1]	0		0
Amounts reclassified from accumulated other comprehensive income (2)	[1]	80		61
Net current-period other comprehensive income	[1]	80		61
Ending balance		(3,894)		(2,116)
Unrealized gains and losses on cash flow hedge
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance		11,303		0
Other comprehensive income before reclassifications	[1]	17,977		4,810
Amounts reclassified from accumulated other comprehensive income (2)	[2]	(722)		0
Net current-period other comprehensive income	[1]	17,255		4,810
Ending balance		$ 28,558		$ 4,810

[1] All amounts are net of tax. Amounts in parenthesis indicate debits.

[2] See following table for details about these reclassifications.